There are currently 222 documents in the archive.

Bibliography Archives List Library Listing

29 July 2012
Added "Space Debris and Its Mitigation" to the archive.
16 July 2012
Space Future has been on something of a hiatus of late. With the concept of Space Tourism steadily increasing in acceptance, and the advances of commercial space, much of our purpose could be said to be achieved. But this industry is still nascent, and there's much to do. So...watch this space.
9 December 2010
Updated "What the Growth of a Space Tourism Industry Could Contribute to Employment, Economic Growth, Environmental Protection, Education, Culture and World Peace" to the 2009 revision.
7 December 2008
"What the Growth of a Space Tourism Industry Could Contribute to Employment, Economic Growth, Environmental Protection, Education, Culture and World Peace" is now the top entry on Space Future's Key Documents list.
30 November 2008
Added Lynx to the Vehicle Designs page.
More What's New Subscribe Updates by Email
M Sonter, , "Equatorial Low Earth Orbit, an ideal orbit for In-Space Construction; and Equatorial Spaceports, as Gateways for Orbital Construction", Asteroid Enterprises Pty Ltd.
Also downloadable from http://www.spacefuture.com/archive/equatorial low earth orbit an ideal orbit for in space construction.shtml

References and Referring Papers    Printable Version 
 Bibliographic Index
Equatorial Low Earth Orbit, an ideal orbit for In-Space Construction; and Equatorial Spaceports, as Gateways for Orbital Construction
Mark Sonter
Large facilities in orbit will need to be assembled from smaller pieces, launched separately. Some of this assembly work will be too complex for automated or teleoperated guidance and will need to be human-directed by spacewalking astronauts. These large facilities may comprise for instance, space solar power satellites, orbital hotels, some sort of zero-g factory facilities, or future space stations tasked with assembly and launch of large spacecraft or other assets to GEO, to the Moon, or to interplanetary destinations (the ideal departure orbit being Equatorial Low Earth Orbit).

Future construction of large facilities in orbit will be most efficiently carried out in Equatorial Low Earth Orbit, ELEO. This is not only because (i) launch due east from the equator has the lowest delta-v requirement of any orbit; but also for reasons of ease of rendezvous: (ii) no need for concern regarding differential orbit plane precession rates for orbits of differing altitudes; and (iii) most importantly, the window for launch to rendezvous with an object already in ELEO orbit re-occurs every 90 minutes. This unequaled ease of rendezvous makes on-orbit delivery logistics very easy and essentially unconstrained, an important issue for construction activities.

Equatorial Low Earth Orbit (ELEO) was identified by the Japanese (eg, Nagatomo et al, 1993) as the orbit of choice for their SPS2000 prototype solar power satellite, for reasons of (i) ease of access vis-a-vis GEO; (ii) less demanding beampointing and focusing requirements than from GEO; (iii) the ability to overfly the same groundsite rectenna every 90 minutes (unavailable to any other orbit, and the next-best thing to being permanently overhead, as with a GEO orbit).

It is assumed that large structure construction will require at least some manned involvement. (This was found to be a crucial need – and a ‘show-stopper’- for assembly of the SPS 2000.) Launches (both of cargo and crew) from a near-equatorial launch site are thus highly desirable.

The usefulness of ELEO was also noted by Brown (1991) in which he raised the concept of beaming microwave energy upward to an orbital industrial park in low equatorial orbit, as a lightweight alternative to solar panel power. He also proposed the beaming of microwave power from Earth to boost ion-powered orbital transfer vehicles delivering satellites from ELEO to GEO or to Earth-escape trajectories.

Facilities, once constructed in ELEO, may then be moved to the final orbit of choice, by being boosted into a highly eccentric orbit, then given any necessary required plane change at apogee with very little delta-v cost, then returned to the desired altitude by use of aerobraking at perigee.

Given that equatorial low earth obit is a desirable location for in-orbit construction, it follows that equatorial launch sites are therefore also necessary. These sites need to be within about 5 degrees of the equator, because the delta-v for plane change becomes ‘too expensive’ at higher latitudes. See table below.


Launch latitude (degrees N or S of Equator)Delta-v for plane change to 0 deg. (km/sec)

0 0
2.5 0.35
5 0.70
7.5 1.05
10 1.39
12.5 1.74

Formula is: delta v = 2 V sin (theta/2) where V is orbital velocity and theta is orbit plane angle to equator.

Launch latitudes above about 5 degrees demand excessive plane change velocity changes.

This ‘latitude constraint’ is much more demanding than for GEOsats, because of the much reduced orbital circular velocity at geosynchronous altitude, and therefore the much lower plane change delta-v demand on the GEOsat Apogee Kick Motor.

Launch sites within 5 degrees of the equator can be considered from the world map below.

Starting from South America, we have the following potential launch site locations, with open sea to the east for ease of recovery of first stage boosters:

  • French Guiana (hosting the Kourou Space Launch Centre); and Brazil (Alcantara Launch Site);
  • Kenya (hosting Italy’s San Marco launch platform);
  • Somalia (politically non-viable failed state);
  • Seychelles and Maldives (very limited land areas available);
  • Eastern Indonesia (Moluccas, Halmahera, West Papua; problems at present of civil instability);
  • Papua New Guinea (PNG) - Sepik, Manus, New Ireland provinces;
  • Nauru (remote, limited facilities, amenities and workforce); Banaba (nil facilities or workforce);
  • Southern Marshall Islands (very limited land; Kwajalein launch site is too far north);
  • Kiribati (remote, small land mass, but Japanese interest in construction of Spaceport); (note SeaLaunch launches from east of Kiribati);

and finally,

  • Galapagos Islands.

Clearly PNG is a location of choice, having a stable and democratic political system, open economy and transparent legal system, availability of an English-speaking technical workforce, and ready air and sea access from both Australia and Japan (and Russia).

There were earlier proposals to develop launch sites in PNG, to launch Protons or Zenits from a site initially to have been on the eastern end of Manus Island and subsequently chosen as Emirau Island, some 250 km east (Flight International 1 Dec 1993). These proposals failed to obtain finance because they were too big, too early, reliant on a single vehicle supplier and reliant on a single market segment ( GEO comsats) that failed to develop as expected.

We (Asteroid Enterprises Pty Ltd together with Papua New Guinean colleagues) propose to revisit these proposals with the relevant authorities, and we envisage initially a small multi-user site with the ability to service all launch azimuths and suborbital as well as orbital launches, and then expanding as launch rate and customer base builds, to eventually fulfill the construction-gateway role described above. We would appreciate any and all feedback.

References:
  1. Nagatomo et al (ed), 30 July 1993, " SPS2000 Project Concept - English Summary", SPS 2000 Task Team, for Solar Power Satellite Working Group, Institute of Space and Astronautical Science.
  2. William C Brown, 1991, " The Equatorial Plane - The International Gateway to Space", Microwave Power Transmission Systems, Weston, Massachusetts, in Space Manufacturing, AIAA 1991.
  3. 1993, "STS in Papua New Guinea: Promoting Proton", Flight International, 1-7 Dec, 1993 pp40-41.
M Sonter, , "Equatorial Low Earth Orbit, an ideal orbit for In-Space Construction; and Equatorial Spaceports, as Gateways for Orbital Construction", Asteroid Enterprises Pty Ltd.
Also downloadable from http://www.spacefuture.com/archive/equatorial low earth orbit an ideal orbit for in space construction.shtml

 Bibliographic Index
Please send comments, critiques and queries to feedback@spacefuture.com.
All material copyright Space Future Consulting except as noted.